Magnetic recording medium and magnetic storage apparatus

Abstract

A magnetic recording medium includes a nonmagnetic substrate, an underlayer disposed above the nonmagnetic substrate, and a magnetic recording layer disposed above the underlayer. The magnetic recording layer includes a first magnetic layer disposed above the underlayer, and a second magnetic layer disposed above the first magnetic layer. Each of the first magnetic layer and the second magnetic layer has a granular structure including magnetic grains having a L1 0 structure and a grain boundary portion. The grain boundary portion of the first magnetic layer includes aluminum nitride, and the grain boundary portion of the second magnetic layer includes hexagonal boron nitride. An aluminum nitride content in the first magnetic layer is in a range of 15 vol % to 35 vol %, and a peak in a B1 s spectrum of the grain boundary portion of the second magnetic layer observed using X-ray photoelectron spectroscopy is 191.6 eV or less.

What is claimed is: 
     
         1 . A magnetic recording medium comprising:
 a nonmagnetic substrate;   an underlayer including at least one NaCl type compound that is MgO, TiO or NiO and disposed above the nonmagnetic substrate; and   a magnetic recording layer disposed on the underlayer, wherein   the magnetic recording layer includes a first magnetic layer disposed on and in contact with the underlayer, and a second magnetic layer disposed above the first magnetic layer,   each of the first magnetic layer and the second magnetic layer has a granular structure including magnetic grains having a L1 0  structure and a grain boundary portion,   the grain boundary portion of the first magnetic layer includes aluminum nitride,   the grain boundary portion of the second magnetic layer includes hexagonal boron nitride,   an absolute value of a Gibbs free energy of oxidation reaction for aluminum included in the grain boundary portion of the first magnetic layer is larger than that for an element, other than aluminum, included in the first magnetic layer and the second magnetic layer,   the second magnetic layer has an intergrain distance that is less than 8.0 nm,   an aluminum nitride content in the first magnetic layer is in a range of 15 vol % to 35 vol %,   a peak in a B1s spectrum of the grain boundary portion of the second magnetic layer observed using X-ray photoelectron spectroscopy is 191.6 eV or less,   the magnetic recording medium has a saturation magnetization that is 688.7 emu/cm 3  or more, and   the element included in the first magnetic layer and the second magnetic layer is B, Fe or Pt, such that the aluminum included in the grain boundary portion of the first magnetic layer is more easily oxidized than the element included in the first magnetic layer and the second magnetic layer and the aluminum reacts with oxygen that diffuses from the nonmagnetic substrate or the underlayer to prevent the oxygen from diffusing into the second magnetic layer.   
     
     
         2 . The magnetic recording medium as claimed in  claim 1 , wherein the first magnetic layer has a thickness in a range of 0.25 nm to 0.7 nm. 
     
     
         3 . The magnetic recording medium as claimed in  claim 1 , wherein the second magnetic layer has a thickness in a range of 5 nm to 12 nm. 
     
     
         4 . The magnetic recording medium as claimed in  claim 1 , wherein the magnetic grains having the L1 0  structure are FePt alloy grains. 
     
     
         5 . The magnetic recording medium as claimed in  claim 2 , wherein the second magnetic layer has a thickness in a range of 5 nm to 12 nm. 
     
     
         6 . The magnetic recording medium as claimed in  claim 2 , wherein the magnetic grains having the L1 0  structure are FePt alloy grains. 
     
     
         7 . A magnetic storage apparatus comprising:
 the magnetic recording medium according to  claim 1 ; and   a head configured to record information on and reproduce information from the magnetic recording medium.   
     
     
         8 . A magnetic storage apparatus comprising:
 the magnetic recording medium according to  claim 2 ; and   a head configured to record information on and reproduce information from the magnetic recording medium.   
     
     
         9 . The magnetic recording medium as claimed in  claim 1 , wherein the grain boundary portion of the first magnetic layer includes SiO 2  in addition to the aluminum nitride.